Hi Neeharika,
So you want to create a whole new process language...Then go to the Tools menu, Resources, Process Languages and click the New icon on the List of Process Language dialog box. Typically when I go about doing a new language, I use a previous one as a template, but you could always start with a blank one.
There is a whole Help document on this topic under Help, Customizing and Extending PowerDesigner, Chapter 1.
HTH,
-Matt C.